14 MASS. EXPERIMENT STATION BULLETIN 324 



The amount of water transpired by crops, together with the percentages of 

 potash contained in them, may be used to show the solubility of potash in the soil. 



Lyon and Bizzell, in Memoir 12 of Cornell University Agricultural Experiment 

 Station, have reported data from which has been calculated the possible con- 

 centration of potash in the water when taken into the plant. Especially striking 

 were their results for the seasons of 1913 and 1914, in two soil tanks, with hay 

 from mixed grasses. The yields of hay and the potash contained in the crops 

 were reported in pounds per acre. The transpiration ratio is the amount of water 

 apparently taken up by the plant in producing a pound of hay. From this ratio 

 was calculated the probable total water taken up by the crop and its concentration 

 in potash. In 1914 the abundant rainfall allowed a liberal supply of water to the 

 growing grass which enabled it to use potash more efficiently than in 1913 and 

 in a more dilute solution. Similar results were obtained with timothy grass in 

 four other soil tanks. 



Table 6. --Potash in transpired water of hay crop, at Ithaca, N. Y. 



1913 1914 



Hay. pounds per acre 4,519 6,063 



Potassium in crop, pounds 41 .4 34.6 



Transpiration ratio 266: 1 408: 1 



Total water, pounds 1,202,000 2,473,000 



Potassium in water, parts per million . . 34 14 



Rainfall, April 1 to August 2 1 , inches 10.15 20 . 72 



Briggs and Shantz of the Bureau of Plant Industry made a comprehensive 

 study of the water used by many different kinds of plants. They reported that 

 the corn plant transpired 415 pounds of water as the maximum and 342 pounds as 

 the minimum for each pound of dry matter built up in the plant. The plants 

 were grown in soil contained in large pots, and water was supplied as liberally 

 as needed by the crops, which varied with the season. 



At this experiment station, numerous analyses of crops have shown approx- 

 imately 1 percent of potash in the dry matter of corn crops. This amount of 

 potash would be equivalent to 24 parts per million parts of water with the max- 

 imum transpiration and 29 parts with the minimum transpiration. 



Availability of Soil Potash for Crops 



Fertilizer experiments in the field, together with chemical analyses of crops in 

 the laboratory, supply data from which may be estimated the availability of the 

 potash naturally present in the soil. 



Morse and Curry found that hay crops on heavy clay loams took from the soil 

 from 60 to 90 pounds of potash per acre, when nitrogen and rainfall were in ample 

 supply. Field G of this experiment station supplied hay crops with from 74 to 

 95 pounds of potash per acre. On the coarser sandy loams of North Soil Test 

 and South Soil Test, hay crops were much influenced by variations in rainfall. 

 In (he favorable seasons, they were able to secure from 40 to 50 pounds of potash 

 per acre. 



Corn on Field G took up 45 to 65 pounds of potash per acre, but on the coarser 

 soils it seldom got more than 25 pounds except when it followed hay crops, the 

 turf of which yielded about twice as much potash. Our fertilizer experiments 

 have shown that the coarser soils were somewhat exhausted of soluble potash 

 after the turf was wholly used. 



